When a mass spectrometer is used for the purpose of proteome analysis, the MSn spectrometry that conducts mass spectrometry over multiple stages becomes important.
As a mass spectrometry method that makes MSn spectrometry possible, there is a three-dimensional quadrupole ion trap mass spectrometer. As disclosed in the patent document 1 (U.S. Pat. No. 2,939,952), the three-dimensional quadrupole ion trap is able to stably accumulate ions having a specific mass-to-charge ratio in the ion trap by applying RF voltage to the ion trap.
Further, the three-dimensional quadrupole ion trap, as disclosed in the patent document 2 (U.S. Pat. No. 4,540,884), makes it possible that accumulated ions in it is scanned with RF voltage amplitude, ions in the ion trap become unstable so as to be ejected sequentially according to mass-to-charge ratio. Mass spectrometry can thus be conducted by sequentially detecting the ejected ions
Furthermore, the three-dimensional quadrupole ion trap, as disclosed in the patent document 3 (U.S. Pat. No. 4,736,101), also makes it possible that with supplemental AC voltage applied separately from RF voltage, only those ions of specific mass-to-charge ratio, which have specific frequency to oscillate resonantly by the supplemental AC voltage, are ejected from the ion trap. Mass resolution can thus be enhanced by detecting those ejected ions and putting them to mass spectrometry.
In addition, the technique disclosed in the patent document 3 (U.S. Pat. No. 4,736,101) permits MSn analysis by means of ion trap, an important analysis for proteome analysis. By resonant oscillation by supplemental AC voltage, all ions having other mass-to-charge ratios than those specific one are ejected from the ion trap, while only the specific ions are isolated in the ion trap. In the next period, the ions isolated by supplemental AC voltage are oscillated resonantly and collide with a bath gas inside the ion trap to induce dissociation of ions. These fragment ions are scanned by ramping voltage amplitude of the RF voltage and ejected sequentially to undergo mass spectrometry. By means of the above technique, it becomes possible to obtain more detailed data on the structure of specimen molecule by the fragmentation pattern.
The quadrupole linear ion trap disclosed in the patent document 4 (U.S. Pat. No. 5,420,425) is also capable of conducting MSn analysis just as the three-dimensional quadrupole ion trap is, and since it has a higher accumulation efficiency than the three-dimensional quadrupole ion trap, increased sensitivity can be realized. Further, mass resolution can be improved space charge effects by accumulated ions are much weaker than the three-dimensional trap.
Further, as disclosed in the patent document 5 (U.S. Pat. No. 6,020,586), a combination of the quadrupole linear ion trap and a time-of-flight mass spectrometer makes it possible to perform MSn analysis and high mass resolution in the time-of-flight mass spectrometer.
Furthermore, as disclosed in the patent document 6 (JP-A 2005-044594), providing a collision damping chamber between the quadrupole linear ion trap and the time-of-flight mass spectrometer improves convergency of energy and positions of ions introduced into the time-of-flight mass spectrometer, which enhances efficiency in introducing ions into the acceleration region of the time-of-flight mass spectrometer, realizing high-sensitivity analysis.
In addition, the disclosure in the patent document 7 (U.S. Pat. No. 5,572,022) is intended to reduce the effect of space charge inside the ion trap. The invention of the patent document 7 describes that time for accumulating ions into the ion trap is adjusted according to the total ion content known from the mass spectrometry conducted just before the introducing process, thereby reducing the effect of space charge inside the ion trap.